In solid structures, particularly in load-bearing structures of, for example, bridges, buildings, tunnels, railways, containment walls, dams, embankments, pipelines and underground structures of metropolitan transport lines, and so on, it is important to monitor, in many points, significant parameters, like, for example, pressure, temperature and mechanical stresses. Such monitoring is carried out periodically or continuously, and is useful both at the initial stage and during the lifetime of the structure.
For this purpose, an approach in this field includes the application of electronic monitoring devices based on electronic sensors, capable of providing good performance at low cost. Usually, such devices are applied onto the surface of the structures to be monitored, or inside recesses already in the structure and accessible from the outside.
Such devices are not able to exhaustively detect the parameters within the structure to be monitored, which it may be useful to know to evaluate the quality of the structure, its safety, its ageing, its reaction to variable atmospheric conditions, and so on. Moreover, such devices can only typically be applied after the structure has been built, and not while it is being built. Therefore, they may be unable to evaluate possible initial or internal defects.
An approach to these requirements is disclosed in U.S. Pat. No. 6,950,767 to Yamashita et al., which provides an electronic monitoring device entirely contained, i.e. “buried”, within the material (for example, reinforced concrete) from which the structure to be monitored is made. More specifically, the device buried in the structure is an entire system encapsulated in a single package, made up of different parts, assembled on a substrate, such as integrated circuits, sensors, antenna, capacitors, batteries, memories, control units, and yet more, made in different chips connected together through electrical connections made with metallic connections.
The system of U.S. Pat. No. 6,950,767 to Yamashita at al. also comprises sub-systems having functions correlated with the power supply, for example, rectifiers in the case in which it receives energy from the outside, through electromagnetic waves, or else its own battery for generating the power supply internally. It may be observed that a monitoring system intended to be “embedded” initially in a building material (for example, liquid concrete, which will then solidify) and to then remain “buried” in the solid structure, is subjected to critical conditions, for example, extremely high pressures, which can even be a few hundreds of atmospheres. There are also numerous other causes of wearing, over time, due, for example, to water infiltration, capable of damaging the system.
A potential drawback to systems, such as that disclosed in U.S. Pat. No. 6,950,767 to Yamashita et al., derives from the fact that they are complex systems, even though they are enclosed in a package, and can therefore be damaged when facing the operating conditions in which they work. In particular, the electrical interconnections between the various parts of the package can be vulnerable. Generally, electrical interconnections inside a harsh environment, such as a concrete structure, are not reliable and have a short lifetime, for example, due to mechanical stress and corrosion.
Moreover, a “window” is provided in the package to allow the sensor to detect an associated parameter can be a weak point for possible infiltration of humidity. Furthermore, a crack or imperfection in the coating material can allow water and chemical substances to penetrate inside the package and cause short-circuits. In addition to water, other substances, such as potentially corrosive acids, can also infiltrate. In general, although designed for the mentioned use, the reliability of systems like that of U.S. Pat. No. 6,950,767 to Yamashita et al. has a limitation due to the complexity of the structure of such systems, although miniaturized. A possible approach is to create an electronic system fully embedded in an integrated circuit without electrical interconnections, but it may need an efficient way to supply power to IC by electromagnetic waves, reducing power loss due to semiconductor material conductivity.